In point-to-point communication, if the transmitter is capable of acquiring certain Channel State Information (CSI), it can optimize the spatial distribution character of modulation mode, code rate and signal power of sending signal, make the sending signal match with channel transmission character, thus realizing the effects of enhancing the reliability of signal reception and reducing requirements of receiver algorithm complexity. In multi-user system, the transmitter can perform scheduling judgment according to acquired CSI, so as to improve the efficiency of system frequency spectrum and avoid the interference among cells.
In LTE (Long-Term Evolution) Rel-8/9, eNB can acquire CSI of downlink channel by using channel reciprocity or UE (User Equipment) feedback; therein, several main transmission modes of PDSCH (Physical Downlink Shared Channel) all adopt implicit CSI feedback method based on codebook. In transmission mode 4, 5 and 6 (as well as PMI (Precoding matrix indication) report mode of transmission mode 8), UE measures downlink channel based on CRS (Cell-specific Reference Signal), reports the number of data stream supported by down link (Rank Indication (RI)) and PMI (Precoding matrix indicator) to eNB according to its own receiving process algorithm, and then reports the Channel Quality Indication (CQI) of each codeword. Therein, UE supposes eNB has used the recommended RI/PMI during the computation process of CQI.
Codebook-based precoding scheme adopted in LTE Rel-8/9 mainly lays emphasis on single-user application scene, while in Rel-10 (LTE-A, viz. LTE-Advanced), precoding and its feedback mechanism will be further optimized to better support multi-user scene. According to current discussion results, LTE-A has the basic requirements for feedback enhancing scheme: try to improve CSI feedback accuracy on the premise of keeping lower feedback overheads. In the aforementioned context, it is basically determined at present that feedback scheme based on double codebook will be adopted in Rel-10. In the scheme, channel information will be divided into two parts: rather stable long-term/broadband CSI and short-term/frequency selective CSI with relative high time/frequency selectivity. UE can quantify the above CSIs by two codebooks in accordance with different feedback cycles, with corresponding PMI fed back. Therein, feeding back PMI-1 of long-term/broadband CSI possesses higher spatial resolution, but it can be fed back in greater cycle and larger bandwidth. PMI-2 is used to reflect the fast part of CSI, which could be in the unit of subband and fed back in lower cycle. As the equivalent channel matrix formed by channel combining with PMI-1 may have lower dimensionality, generally PMI-2 only needs to quantify the CSI with lower dimensionality, thus few bit of PMI-2.
In the present version (Rel-8/9) of LTE, higher layer can configure UE to perform periodical report by adopting PUCCH (Physical uplink Control Channel) and/or aperiodic report by PUSCH (Physical Uplink Shared Channel). According to present specifications and the Way forward reached in current LTE-A discussion, the report contents and processes of PUCCH and PUSCH shall be totally independent. Table 1 and Table 2 show the report modes in present specifications based on PUCCH and PUSCH respectively. Among them, PUCCH report mode refers to the combination of PUCCH report type, with the correspondence shown in Table 3.
TABLE 1PUCCH-based Report ModePMI Feedback TypeSingleNo PMIPMIPUCCH CQIWidebandModeMode 1-1Feedback Type(wideband CQI)1-0UE SelectedModeMode 2-1(subband CQI)2-0
TABLE 2PUSCH-based Report ModePMI Feedback TypeMultipleNo PMISingle PMIPMIPUSCH CQIWidebandMode 1-2Feedback Type(wideband CQI)UE SelectedMode 2-0Mode 2-2(subband CQI)HigherMode 3-0Mode 3-1Layer-configured(subband CQI)
TABLE 3Report Type and Bit Number Included in Each PUCCH Reporting ModePUCCHPUCCH Reporting ModesReportMode 1-1Mode 2-1Mode 1-0Mode 2-0TypeReportedMode State(bits/BP)(bits/BP)(bits/BP)(bits/BP)1Sub-bandRI = 1NA4 + LNA4 + LCQIRI > 1NA7 + LNA4 + L2Wideband2 TX Antennas RI = 166NANACQI/PMI4 TX Antennas RI = 188NANA2 TX Antennas RI > 188NANA4 TX Antennas RI > 111 11 NANA3RI2-layer spatial multiplexing11114-layer spatial multiplexing22224Wideband CQIRI = 1 or RI > 1NANA44
In course of implementing the present invention, the inventor finds out there are at least the defects below in the present technology:
On one hand, the present feedback mechanism fails to realize double-stage feedback; on the other hand, the report contents and processes of PUCCH and PUSCH shall be totally independent in the present feedback mechanism, but actually the information provided by the two report paths may have some redundancy. If double codebook feedback is supported simultaneously in PUCCH and PUSCH, it is inevitable to increase new reporting mode. Besides, feedback overheads may be increased if double-stage feedback is to be independently supported in PUCCH and PUSCH.